Electrostatic filters are well known in the art both for home and industrial use. Such filters typically employ wires which are maintained at a high potential and are designed to trap particles in the air. These filters have been used in conjunction with mechanical filters designed to trap particles of relatively gross size. Particles of a smaller size are then passed through an electrostatic filter which is located at a point downstream with respect to the air flow. Filter systems of this type are found in many forced air systems for home use and in clean rooms used, for example, in semiconductor manufacture.
In the semiconductor industry particularly, the demand for systems which remove smaller and smaller particles from the air is acute. This requirement arises from the fact that as integrated circuits are made smaller and smaller, they suffer increasingly significant damage from airborne contaminants of smaller and smaller size. These contaminants decrease yields of semiconductor devices and thus increase cost. The elimination of smaller and smaller airborne particles is a major concern to the semiconductor industry.
In the semiconductor industry, besides elimination of small airborne particles, it is likewise a major concern to be able to eliminate contaminants from the various liquids which are utilized in the semiconductor manufacturing process. While it is of course necessary not to obstruct air flow in an air filter, it is perhaps even more important not to obstruct fluid flow in a liquid filter.
In the prior art, materials which have been used for liquid filters (e.g., in the integrated circuit arts) tended to block the flow of liquid and further tended to clog. Such prior art filters for liquids relied on the mechanical process of driving the liquid through a relatively fine mechanical mesh. Contaminating particles larger than the openings of the mesh would be mechanically trapped therein. The accumulation of particles on such a mesh screen would create a large pressure drop at the filter and a great deal of wear and tear on the filter. Such wear and tear on the filter can destroy parts of the filter which in turn can create still further contaminating particles. In addition, such prior art mesh filters were inadequate for capturing very small particles. The clogging of such filters resulted in having to frequently change such filters. Additionally, the clogging of such filters often created a deleterious back pressure in the system.
The present invention provides a filter which exhibits very little resistance to the material moving through it and yet is extremely effective in removing particles from the material. The present invention also provides a filter which is useful in the process of manufacturing integrated circuits and other products to eliminate contaminating particles from liquids which are used in the manufacturing process, e.g., any chemicals which are to come into contact with an integrated circuit wafer. The present invention still further provides such a liquid filter which has relatively large holes within it for permitting the liquid to flow easily therethrough while destroying the contaminating particles within the liquid. The improved electrostatic fluid filter of the present invention is tubular in construction and has an inlet port for supplying fluid to be filtered and an output port from which relatively pure fluid flows. The filter includes a high voltage conductor which is disposed along the axis of the tube and which is surrounded by a ridged insulator. Fluid is directed along the length of the filter parallel to the conductor. Contaminating particles in the fluid are transformed into electrical dipoles and are attracted to the high voltage conductor.